As an example of related art of a wireless sensor-equipped bearing, there is known a wireless sensor-equipped bearing having, as a power generation mechanism, electromagnetic induction which causes an induction current in a coil by a magnetic flux density variation due to relative rotation between a magnet and a coil which are provided in the inside of the bearing (see, for example, PTLs 1 to 4).
The wireless sensor-equipped bearing having electromagnetic induction as a power generation mechanism includes a circuit configured to supply an electric current, which is generated in the coil by electromagnetic induction, to a power-supplied unit, and a circuit configured to convert detection information detected by a sensor to a wireless signal. PTLs 1-4 are silent on measures to reduce noise caused on these circuits due to the electromagnetic induction.
In addition, in the wireless sensor-equipped bearing described in PTL 3, a sensor unit is provided on a seal which seals the bearing space of a rolling bearing. This sensor unit includes a sensor configured to detect information of the state of the rolling bearing; information handling means for handling the information detected by the sensor; and a power supply having a power generation function which can drive the information handling means and the sensor.
Specifically, it can be said that the invention described in PTL 3 aims at obtaining a wireless sensor-equipped bearing having a power generation function, by simply replacing the seal of a conventional rolling bearing with a sensor unit-equipped seal.
However, PTL 3 describes that, as regards the power supply, it is possible to apply power generation mechanisms which use a Seebeck element that is a thermoelectric power generating element, or an electret element that is a vibration power generating element. In these power generation mechanisms, at a low-speed rotation time at an initial stage of use of the rolling mechanism, it is difficult to obtain necessary power since the temperature difference between the obverse and reverse surfaces of the seal or the vibration occurring in the seal is small.
In addition, PTL 4 discloses technology in which an annular magnet having N poles and S poles arranged alternately in the circumferential direction is fixed to one of an inner ring and an outer ring. An annular conductor, which is opposed to this magnet in the axial direction, is fixed to the other of the inner ring and outer ring, and electromotive force is generated by relative rotation between the magnet and conductor. This annular magnet and this conductor are required in addition to the structural parts of the conventional rolling bearing.